Programmed cell death, or apoptosis, is an essential feature of growth and development, as the control of cell number is a balance between cell proliferation and cell death. Apoptosis is an active rather than a passive process, resulting in cell suicide as a result of any of a number of external or internal signals. Apoptotic cell death is characterized by nuclear condensation, endonucleolytic degradation of DNA at nucleosomal intervals ("laddering") and plasma membrane blebbing. Programmed cell death plays an essential role in, for example, immune system development and nervous system development. In the former, T cells displaying autoreactive antigen receptors are removed by apoptosis. In the latter, a significant reshaping of neural structures occurs, partly through apoptosis.
An increasing number of genes and gene products have been implicated in apoptosis. One of these is bcl-2, which is an intracellular membrane protein shown to block or delay apoptosis. Overexpression of bcl-2 has been shown to be related to hyperplasia, autoimmunity and resistance to apoptosis, including that induced by chemotherapy (Fang et al., J. Immunol. 1994, 153, 4388-4398). A family of bcl-2-related genes has been described. All bcl-2 family members share two highly conserved domains, BH1 and BH2. These family members include, but are not limited to, A-1, mcl-1, bax and bcl-x. Bcl-x was isolated using a bcl-2 cDNA probe at low stringency due to its sequence homology with bcl-2. Bcl-x was found to function as a bcl-2-independent regulator of apoptosis (Boise et al., Cell, 1993, 74, 597-608). Two isoforms of bcl-x were reported in humans. Bcl-xl (long) contains the highly conserved BH1 and BH2 domains. When transfected into an IL-3 dependent cell line, bcl-xl inhibited apoptosis during growth factor withdrawal in a manner similar to bcl-2. In contrast, the bcl-x short isoform, bcl-xs, which is produced by alternative splicing and lacks a 63-amino acid region of exon 1 containing the BH1 and BH2 domains, antagonizes the anti-apoptotic effect of either bcl-2 or bcl-xl.
As numbered in Boise et al.,Cell, 1993 74:, 597-608, the bcl-x transcript can be categorized into regions described by those of skill in the art as follows: nucleotides 1-134, 5' untranslated region (5'-UTR); nucleotides 135-137, translation initiation codon (AUG); nucleotides 135-836, coding region, of which 135-509 are the shorter exon 1 of the bcl-xs transcript and 135-698 are the longer exon 1 of the bcl-xl transcript; nucleotides 699-836, exon 2; nucleotides 834-836, stop codon; and nucleotides 837-926, 3' untranslated region (3'-UTR). Between exons 1 and 2 (between nucleotide 698 and 699) an intron is spliced out of the pre-mRNA when the mature bcl-xl (long) mRNA transcript is produced. An alternative splice from position 509 to position 699 produces the bcl-xs (short) mRNA transcript which is 189 nucleotides shorter than the long transcript, encoding a protein product (bcl-xs) which is 63 amino acids shorter than bcl-xl.
Diseases and conditions in which apoptosis has been implicated fall into two categories, those in which there is increased cell survival (i.e., apoptosis is reduced) and those in which there is excess cell death (i.e.,apoptosis is increased). Diseases in which there is an excessive accumulation of cells due to increased cell survival include cancer, autoimmune disorders and viral infections. Until recently, it was thought that cytotoxic drugs killed target cells directly by interfering with some life-maintaining function. However, of late, it has been shown that exposure to several cytotoxic drugs with disparate mechanisms of action induces apoptosis in both malignant and normal cells. Manipulation of levels of trophic factors (e.g., by anti-estrogen compounds or those which reduce levels of various growth hormones) has been one clinical approach to promote apoptosis, since deprivation of trophic factors can induce apoptosis. Apoptosis is also essential for the removal of potentially autoreactive lymphocytes during development and the removal of excess cells after the completion of an immune or inflammatory response. Recent work has clearly demonstrated that improper apoptosis may underlie the pathogenesis of autoimmune diseases by allowing abnormal autoreactive lymphocytes to survive. For these and other conditions in which insufficient apoptosis is believed to be involved, promotion of apoptosis is desired.
In the second category, AIDS and neurodegenerative disorders like Alzheimer's or Parkinson's disease represent disorders for which an excess of cell death due to promotion of apoptosis (or unwanted apoptosis) has been implicated. Amyotrophic lateral sclerosis, retinitis pigmentosa, and epilepsy are other neurologic disorders in which apoptosis has been implicated. Apoptosis has been reported to occur in conditions characterized by ischemia, e.g. myocardial infarction and stroke. Apoptosis has also been implicated in a number of liver disorders including obstructive jaundice and hepatic damage due to toxins and drugs. Apoptosis has also been identified as a key phenomenon in some diseases of the kidney, i.e. polycystic kidney, as well as in disorders of the pancreas including diabetes (Thatte, et al., Drugs, 1997, 54, 511-532). For these and other diseases and conditions in which unwanted apoptosis is believed to be involved, inhibitors of apoptosis are desired.
Antisense oligonucleotides have been used to elucidate the role of several members of the bcl-2 family. Extensive studies using antisense oligonucleotides targeted to bcl-2 have been performed, and an antisense compound (G3139, Genta Incorporated) targeted to human bcl-2 has entered clinical trials for lymphoma and prostate cancer.
Amarante-Mendes et al., Oncogene, 1998, 16, 1383-1390, disclose antisense oligonucleotides targeted to bcr and bcl-x. The latter downregulated the expression of bcl-xl and increased the susceptibility of HL-60 Bcr-Abl cells to staurosporine.
U.S. Pat. No. 5,583,034 (Green et al.) discloses antisense oligonucleotides which hybridize to the nucleic acid sequence of an anti-apoptotic gene, preferably to the translation start site of bcr-abl.
Wang et al. used a phosphorothioate oligonucleotide targeted to the bcl-x translation start site to block CD40L-mediated apoptotic rescue in murine WEHI-231 lymphoma cells (J. Immunol., 1995, 155, 3722-3725).
Fujio et al. have used an antisense oligodeoxynucleotide targeted to murine and rat bcl-x mRNA to reduce bcl-xl protein expression (J. Clin. Invest., 1997, 99, 2898-2905). The compound tested was the same as that of Wang et al. Oligonucleotide treatment inhibited the cytoprotective effect of leukemia inhibitory factor in mouse or rat cardiac myocytes.
Pollman et al. used antisense oligodeoxynucleotides with phosphorothioate backbones to downregulate bcl-xl expression in blood vessel intimal cells (Nature Med., 1998, 4, 222-227). This resulted in induction of apoptosis and regression of vascular lesions. Antisense sequences were targeted to the translation initiation codon of mouse/human bcl-x (conserved sequence) and were used in rabbits. Gibbons et al., U.S. Pat. No. 5,776,905, disclose methods for targeted deletion of intimal lesion cells in the vasculature of a mammal with vascular disease, preferably with antisense molecules specific for anti-apoptotic genes, more preferably bcl-x and most preferably bcl-xl.
Thompson et al., U.S. Pat. No. 5,646,008 and WO 95/00642 describe an isolated and purified polynucleotide that encodes a polypeptide other than bcl-2 that promotes or inhibits programmed vertebrate cell death. Preferably the polypeptide is bcl-xl, bcl-xs or bcl-x.sub.1. Polypeptides, polynucleotides identical or complementary to a portion of the isolated and purified polynucleotide, expression vectors, host cells, antibodies and therapeutic and diagnostic methods of use are also provided.
Yang et al., WO 98/05777 disclose bcl-x.gamma. (gamma), at novel isoform of the bcl-x family which includes an ankyrin domain. Polypeptide and nucleic acid sequences for this isoform are disclosed, as well as, inter alia, methods for modulating bcl-xy activity, including antisense methods.